Add full compiler toolchain, libc, examples and reference docs

First substantive commit: the entire Sprinter C compiler tree on top of
the bare README+gitignore initial commit.

What's in here:
  bin/sprinter-cc        — driver script invoking SDCC + linker + mkexe
  libc/                  — Sprinter-specific libc layer over ESTEX/BIOS
                           (conio, gfx, io, mem, stdio + headers)
  runtime/               — crt0 variants (default/small/banked/minimal)
                           + heap + bank trampolines
  toolchain/             — mkexe (SprintEXE packer, C + tests)
  examples/              — 30 demo programs (gfx, file I/O, env, time, …)
  lib/Makefile           — builds the libc archive (sprinter.lib)
  docs/                  — converted Sprinter manuals + asm reference samples
  third_party/           — solid-c reference compiler dump + sdcc setup script
  release_docs/          — packaging / release notes

gitignore overhaul:
  • Drop dangerous blanket patterns: *.asm (would hide docs/samples/*.asm)
    and *.exe (case-insensitive match was hiding third_party/solid-c/*.EXE
    on macOS APFS).  Replaced with examples/*/*.{asm,exe,…} and lib/*.lib.
  • Restore tracking of toolchain/mkexe/tests/{one,big}.bin — those are
    INPUT fixtures, not build outputs.
  • Collapse the duplicated SDCC/C/Sdcc sections into one section per
    concern (build outputs / vendored / OS-junk).
  • Add .sprinter-cc-*/, build/ (catches lib/build/ too), .claude/.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

docs/reference/SPRINT2K/sprn2k61.txt

@@ -0,0 +1,35 @@
+*** Area: ZX.SPECTRUM                             Date: 20 Jan 03 15:47:07
+*** From: Ivan Mak (2:5030/529.24)
+*** To  : Maxim Timonin
+*** Subj: Sprinter
+
+        �ਢ¥âáâ¢ãî ‚ á, Maxim!
+
+  <Monday January 20 2003> <01:19> Maxim Timonin wr®te to Ivan Mak:
+
+ >> ‚ë¡®p ¡ë« ᤥ« ­ ¯® ¯p¨­æ¨¯ã: "å®çã ‘¯¥ªâpã¬". ‡­ ç¨â -> Z80.
+ >> € á ¬®â®p®«®© €¬¨£  ¯®«ã稫 áì ¡ë... ‘ ¯¥­â¨ã¬®¬ - �–...
+
+ MT> € ¯®ç¥¬ã ­¥ ¡ë« ¢§ïâ ¯à®æ Z180? ˆ«¨, ᪠¦¥¬ Z380, ª ª, ­ ¯à¨¬¥à, ¢
+ MT> ­¥¤®¤¥« ­­®¬ AZX? ‘ ®¤­®© áâ®à®­ë ¨ ᮢ¬¥á⨬®áâì á Z80 ¤«ï áâ àëå
+ MT> ¯à®£à ¬¬, á ¤à㣮© áâ®à®­ë 32-¡¨â­ ï à §à來®áâì ¯à¨ à ¡®â¥ ­  ¯®«­ãî
+ MT> ª âãèªã, ᪮à®áâì ¢ á।­¥¬ ­  33Œƒæ (ᥩç á á«ëè «, ç⮠㦥 á¢ëè¥
+ MT> 50Œƒæ ¯®«ãç îâ). ‚®â íâ® ¡ë ¤¥©á⢨⥫쭮 ¡ë«® ¡ë ¯à®¤®«¦¥­¨¥ à §¢¨â¨ï
+ MT> ¢¥â¢¨ ᨭª«¥à-ª«®­®¢? ­®¢ ï  àå¨â¥ªâãà , ­®¢ë© ¯à®¤¢¨­ãâë© ¯à®æ...
+
+Z180 ­¥ ᮢ¬¥á⨬ á® ‘¯¥ªâp㬮¬. ’ ¬ ¯p®¡«¥¬ ¡®«ìè¥ ç¥¬ ¯«îᮢ, ¯® ᥬ㠮­ ¡ë«
+®â¡p®è¥­ áp §ã. € Z380 ­¥ ¡ë« ¢§ïâ, ¯®â®¬ã çâ® ¡ë« ᨫ쭮 ¤®p®£ (ª ⮬㠦¥, ®­
+á­ p㦨 16 ¡¨â,   32 ⮫쪮 ¢­ãâp¨). ˆ ᥩç á ¥£® ¢®¢á¥ ¯p¥ªp â¨«¨ ¢ë¯ã᪠âì,
+â ª çâ® ‘¯p¨­â¥p ®ª § «áï ¡ë á ­¨¬ ¢ ¯p®«¥â¥. Zilog ¢ë¯ãá⨫  eZ80, ¢®â ®­ ­ 
+50MHz ¨ ¥áâì. ’®«ìª® ®¯ïâì ¦¥ ᮢ¬¥á⨬®áâì ã ­¥£® ­¥ ¯®«­ ï. Hã, ­¥¢¤®¬¥ª
+Zilog-ã, çâ® ªâ®-â® ­  ¥£® ¯p®æ å ¥é¥ ‘¯¥ªâpã¬ë ᮡ¨p ¥â, ¨ ¯®«ãç ¥âáï, çâ®
+¢ ¦­ë¥ ᯥªâp㬮¢áª¨¥ ¯®pâë - § ­ïâë. H¥¤®ª.ª®¬ ­¤ë ¨§¬¥­¥­ë ¨ â.¤. ¨ â.¯.
+
+
+        �à®â®áë á¡¥¦ «¨. ‡¥à£¨ § ª®¯ «¨áì. �®à  ¨ ¬­¥ § ªà㣫ïâìáï. Ivan.
+
+ - � §¢®¤¨áì á奬ª , ¡®«ìè  ¨ ¬ «¥­ìª ... [Sprinter] Sprinter-II [Forth-CPU]
+
+... ivan_mak@mail.ru  *  http://winglion.spb.ru  *  http://www.petersplus.ru
+--- GoldED+/386 1.0.0
+ * Origin: The Sprinter has You! (2:5030/529.24)